1. Field of the Invention
The present invention relates to a hologram recording and reproducing device and a method for recording a hologram.
2. Description of the Related Art
In recent years, a hologram recording and reproducing device has attracted attention as a data storage device. To record a hologram, reference light and data light are generated from laser light output from a single light source. In this case, the data light is modulated on the basis of recorded data. A hologram recording medium is irradiated with the reference light and the data light. The reference light and the data light interfere with each other in the hologram recording medium to form the hologram (diffraction grating). The hologram is recorded in the hologram recording medium. The recorded hologram includes a large amount of information. To reproduce the recorded information from the hologram recording medium, the hologram is irradiated with the reference light to ensure that reproduction light (diffracted light) is generated. The reproduction light is received by an imager having light receiving elements two-dimensionally arranged. Then, signal processing is performed on the reproduction light to reproduce the recorded data.
In the aforementioned case, the data light and the reference light are generated by an optical unit having optical elements, and the reproduction light is received by the optical unit. A certain optical unit has a common optical path through which data light and reference light pass. That is, the certain optical unit has a coaxial interference system (refer to Japanese Patent Publication No. 2003-178484). In addition, another optical unit has an optical path through which data light passes and an optical path through which reference light passes. The two optical paths are different from each other. That is, the optical unit has a two-beam interference system. As an optical source that is adapted to generate an optical beam and used in a hologram recording and reproducing device, there is a proposed technique related to an external cavity laser that emits a blue optical beam (refer to Japanese Patent Publication No. 2006-177995). In addition, there is a proposed technique for recording a hologram under the condition that a hologram recording medium moves (refer to Japanese Patent Publication No. 2007-178780). Furthermore, recording and reproducing characteristics obtained when an external cavity semiconductor laser is used have been reported (refer to “T. Tanaka, K. Takahashi, K. Sato, R. Kasegawa, M. Toishi, K. Watanabe, D. Samuels, and M. Takeya, “Littrow-type external-cavity blue laser for holographic data storage,” Appl. Opt. 46, 3583-3592 (2007)”).